My ordered truck is coming with a 6 speed and the 3.55 (supposedly?) but my dealer currently has the identical truck only it has the 8 speed and the 3.21 gear ratio.

I don't tow a lot but don't want a dog off the line either.

My current 09 Sierra with a 5.3ci 4 speed and 3.73 is somewhat a dog off the line, but I think it has more to do with the ECM than anything else?

I was hoping for an 8 speed with my current on order truck but at time of ordering I was told it wasn't available, but with my current 4 speed GM and the 3.73 gear ratio, the 6 speed with the 3.55 should at least give me better gas mileage, I hope?